Persistent supersaturations for condensation growth of particles

Abstract

Apparatus designed to produce enlarged particles by condensation growth in a stream, comprising: a tubing coil having an inner surface defining a tubing cross-section, the tubing coil having a coil diameter (A), the tubing (1400) having a current-receiving inlet and an outlet, the tubing (1400) having a length between the inlet and the outlet; a heater (1104) configured to heat the tube (1400) along a first longitudinal portion of the tube cross-section, the first longitudinal portion of the tube cross-section having a first arcuate location relative to a cross-section of the tube (1400) along the length of the tube (1400); and a cooler (1106) configured to cool the tube (1400) along at least a second longitudinal portion of the tube cross-section, wherein the second longitudinal portion of the tube cross-section has a second arcuate location with respect to a cross-section of the tube (1400) along the length of the tube (1400).

Description

BACKGROUND

[0001] Condensation growth systems have been used to enlarge submicrometer-sized aerosolized particles to form droplets. These aerosolized particles may be suspended or entrained by another process gas, such as nitrogen, but are defined as particles containing condensed matter (liquid or solid) suspended in a gas that is too small to settle by gravity over the timescales of interest. Often, the diameter of the aerosolized particles of interest is less than a few micrometers. To facilitate their measurement, these particles can be grown by condensation to form larger droplets that can be detected or manipulated much more easily than the original particle. For example, the droplets can be optically detected, inertially captured, or aerodynamically focused.

[0002] For small particles, condensation growth is initiated by exposing the particle to a vapor supersaturation region, defined as the region where the vapor pressure of the condensing vapor over a flat surface is higher than its saturation value. These supersaturated conditions are used because the equilibrium vapor pressure over the curved surface of an ultrafine particle is higher than over a flat surface of the same chemical composition. This is due to the energy associated with surface tension, a phenomenon described by the Kelvin relationship. Water condensation onto small particles requires relative humidity values ​​above 100%. Roughly speaking, the relative humidity required to activate condensation growth of particles with a diameter below 6 nm is in the range of 140% and above.The exact value of the required supersaturation also depends on the particle chemistry, which for soluble salts is described by the Kohler relations.

[0003] Supersaturated conditions at the walls of the flow-carrying vessel are not possible, as any excess water vapor simply settles on the walls. However, it is possible to create non-equilibrium conditions in the core of the flow, providing temporarily supersaturated conditions. Methods for achieving this include (1) adiabatic expansion of a saturated flow, (2) the rapid (generally turbulent) mixing of flow streams at different temperatures, and (3) laminar flow diffusion, where a cooler flow is introduced into a warm, moist-walled tube.

[0004] In each of these processes, the time the stream experiences supersaturated conditions is limited. In laminar flow processes, for example, the supersaturation profiles exhibit a steep maximum followed by a decline. Since the majority of condensation growth occurs in this peak supersaturation region, this limited time also limits the size of the droplet that is formed. This is particularly problematic when operating at low supersaturations, such as those typical of clouds. Furthermore, the activation of condensation growth may be kinetically limited, so that this brief supersaturation is not sufficient to initiate condensation growth on particles that are hydrophobic, i.e., those that have an inherently low probability of water molecules attaching to their surface. WO 2005 / 066610 A1 discloses an apparatus and method for enlarging small particles.WO 2011 / 047219 A2 describes a method for counting particles in a gas. The publication by DRAVID, AN [et al.]: Effect of secondary fluid motion on laminar flow heat transfer in helically coiled tubes. In: AIChE journal, Vol. 17, 1971, No. 5, pp. 1114-1122. ISSN 1547-5905. DOI: https: / / doi.org / 10.1002 / aic.690170517 [accessed on 2024-11-05] describes the effects of secondary fluid motion on laminar flow heat transfer in helically coiled tubes. SUMMARY

[0005] Briefly described, the invention relates to an apparatus and a method for generating enlarged particles in a stream according to the independent claims. The apparatus includes a coiled tubing having a tube diameter and a coiled diameter, the tube having a stream-receiving inlet and an outlet, the tube having a length between the inlet and the outlet. A heater is configured to heat a first longitudinal portion of the tube along a first portion of the tube diameter, the first portion of the tube diameter having an approximately constant location relative to a cross-section of the tube along the length of the tube. A cooler is configured to cool a second longitudinal portion of the tube along at least a second portion of the tube diameter, the second portion of the tube diameter being in an approximately constant position along the length of the tube.The coiled tubing contains inner walls designed to be wetted throughout with a condensing fluid.

[0006] The method comprises providing a tubing coil having a tube diameter and a coil diameter, the tube having an inlet receiving an input flow and an outlet, the tube having a length between the inlet and the outlet. Thereafter, the method comprises heating a first longitudinal portion of the tube along a first portion of the tube diameter, the first portion of the tube diameter being at a constant position along the length of the tube, and simultaneously cooling a second longitudinal portion of the tube along at least a second longitudinal portion of the tube diameter, the second portion of the tube diameter being at a constant position along the length of the tube. The method comprises, during the heating and cooling, introducing a flow into an interior of the tube at an inlet, the flow moving toward the outlet.

[0007] This Summary is provided to introduce, in simplified form, a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1A illustrates a first embodiment of a device according to the present technology comprising a straight growth tube. Fig. Figure 1B represents a cross-section of the straight growth tube along line 1B-1B. Fig. Figure 2 represents the saturation ratio for one layer of current in the straight growth tube of Fig. 1 in operation. Fig. 3A and Fig. 3B are graphs showing the saturation ratio at several radial positions from a vertical layer of a 0.3 l / min airflow in the device of Fig. 1A for 50% RH and 0% RH respectively. Fig. Figure 4 illustrates a second embodiment of the technology having a flat coil growth tube in a single plane with the top side being warmer than the bottom side. Fig. 5 is a cross-section of the facility of Fig. 4, which shows the velocity fields of the helix, showing secondary current patterns. Fig. Figure 6 represents the saturation ratio for a layer of current in the device of Fig. 4, which extends between the warm and cold surfaces. The Fig. 7A and Fig. 7B are diagrams showing the saturation ratio at several radial positions from the vertical layer of Fig. 6 for a 0.3 l / min air flow entering at 0% RH or 50% RH. Fig. Figure 8A illustrates another embodiment of the technology, depicting a helical growth tube having a spiral coil, with the inside and outside of the coil at different temperatures. Fig. 8B is a cross section along line 8B-8B in Fig. 8A. Fig. Figure 9 represents the saturation ratio for the layer of current located between the warm and cold surfaces of the growth tube of Fig. 8A. Fig. Figure 10 is a graph showing the saturation ratio as a function of axial position for several radial positions for the helical configuration of Fig. 8A. Fig. Figure 11A is a side view showing a condensation growth spiral of Fig. 4A, which is contained in a particle collector or a particle counter. Fig. 11B is a perspective view showing the setup of Fig. 4, which is configured as an optical detector with an optical head. Fig. 11C is a perspective view of the facility of Fig. 13B with heating element removed. Fig. 11D is a perspective view of the facility of Fig. 11A, which is configured as a particle collector. Fig. 12 is a perspective view of another embodiment including a growth tube coil wherein a first portion of the coil has circumferentially uniformly cooler walls than a second portion has circumferentially uniformly warmer walls. Fig. Figure 13 is a diagram showing a comparison between a straight growth tube and a spiral growth tube. Fig. 14A and Fig. 14B are perspective and cross-sectional views of a general device formed in accordance with the present technology and including an inlet, a growth tube coil, an outlet, a droplet measuring or manipulating device, and a pump, fan, or other flow moving device. DETAILED DESCRIPTION

[0008] A technology is presented that relates to a method for enlarging suspended particles by condensation growth through water or other vapor to form droplets that can be easily detected optically, picked up by inertia, or aerodynamically focused.

[0009] A growth tube structure and a method of operating a growth tube are provided. The method and apparatus of the present technology provide a "growth tube sandwich" with various configurations in which flow moves in an axial direction along a wet-walled tube whose wall temperatures vary with angular position but are generally constant over much of the length of the tube with the axial location. In this context, "constant" means that the angular position of the heated and cooled portions referred to herein may vary by one or more degrees, but remain within the upper or lower half of the tube cross-section along the length of the tube. Walls within angular positions of approximately 20-160° (with respect to a common origin), for example, may be warm, while those along angular positions of approximately200-340° (relative to a common origin at 0°) are cold. Intermediate radial positions in regions (e.g., at 0°±20° and 180°±20°) are transition regions with intermediate temperatures. This same angle-dependent wall temperature profile extends over most of the length of the tube and is fixed over a large portion of its axial extent. This tube can be configured as a straight tube, a flat coil, or a helix.

[0010] This configuration creates a region in the middle part of the flow where the local vapor pressure of the fluid wetting the walls is higher than the equilibrium value of the fluid at the local temperature. As the flow moves down the tube, the vapor pressure and temperature profiles approach a steady state, with the saturation ratio (defined as the ratio of vapor pressure to equilibrium vapor pressure) being nearly independent of axial location, depending only on radial and angular positions. These flow curves with a nearly constant, high saturation ratio provide longer activation times and stronger particle growth than previous laminar flow methods. This approach is particularly effective when the diffusivity of the condensing fluid and the thermal diffusivity of the carrier gas are similar, as is the case, for example, with water condensation onto airborne particles.

[0011] A first embodiment of the growth tube device according to the present technology is a straight tube 100 as shown in Fig. 1A. A device for operation with the tube 100 of Fig. 1A may further include one or more input devices providing current to the input end 115 and output devices coupled to an opposite end of the growth tube 100, examples of which are described with reference to FIG. Fig. 11A - 11D. It should be clarified that the input and output devices of the Fig. 11A-11D may be used with any of the growth tube device embodiments described herein.

[0012] In Fig. 1A, a dark and light shade indicates a temperature difference, with a lighter shade indicating warmer temperatures and a dark shade indicating colder temperatures according to the graph on the right side of Fig. 1A shown scale.

[0013] The inner walls of the tube 100 are completely wetted with the condensing fluid. As shown in the Fig. 1A and Fig. 1B, one side 110 of the tube 100 is warmer than the other side. In the illustration of Fig. 1A, Fig. 1B, the wall in region 110 is maintained at 60°C at angular positions of approximately 20° to 160°, and the wall in region 112 is maintained at 60°C at angular positions of 200° to 340° in region 112 extending by an axial distance greater than or equal to the volumetric flow rate multiplied by 0.5 s / cm 2 is kept at 20°C. The angular positions are referred to a common origin in the center of the tube (in Fig. 1B at 0°), and the angular positions (an origin) and thus regions 110 and 112 are constant along the length of tube 100, thereby extending longitudinally along the length of the tube. It should be apparent that a particle stream with an ambient temperature of approximately 22°C can be introduced into tube 100 via the inlet end 115 of tube 100. Air flow enters at opening 115 at the bottom left and moves in the Z direction. The walls are consistently wetted with the liquid phase of the condensing vapor. Intermediate radial positions in regions 116 and 118 (0°±20° and 180°±20°, respectively) can be provided as transition regions with intermediate temperatures.

[0014] In an alternative embodiment, the region 110 may be greater than 140°, so that the region 110 extends halfway down the tube 100 and the region 112 also extends halfway down the tube 100, with the transition regions 116 and 118 being reduced to a minimum.

[0015] Calculations were made for the configuration of Fig. 1A-1B were carried out for the case of water condensation. The inner walls are wetted with water. The tube has an inner diameter D1 of 6 mm and carries an air flow of 0.3 l / min. Under these conditions, the flow is laminar, and transport occurs by convective diffusion. The temperature differences between the opposite sides of the tube create a temperature gradient. There is also a gradient in the vapor profile. Near the inlet 115 of the tube, the vapor pressure and temperature profiles evolve with the axial location, as does the saturation ratio. Further along the tube, these parameters approach steady-state values, which are maintained for the remainder of the tube length.

[0016] In this region near steady-state, the saturation ratio values ​​near the centerline exceed one. These "supersaturated" conditions (i.e., a saturation ratio greater than 1) arise from the differences in the rates of vapor mass and heat transfer from the walls into the stream, as well as the nonlinear dependence of the equilibrium vapor pressure on temperature.

[0017] The ones for the Fig. 1A-1B calculated saturation profiles are shown in the Fig. 2, Fig. 3A and Fig. 3B shown. Fig. Figure 2 shows the saturation ratio for a layer 202 of the current, where the layer is located between the warm and cold surfaces of the growth tube of Fig. 1. The layer shown lies in the xz-plane at the y-axis position of y=0 and extends between the warm 110 and cold 112 surface of the growth tube of Fig. 1. In disk 202, higher saturation ratios are indicated by a lighter shade, and lower saturation ratio values ​​are darker, according to the scale on the right. The tube diameter is 6 mm and the flow rate is 0.3 l / min. The condensing vapor is water, the carrier gas is air, and the incoming stream is at 22°C and 50% RH.

[0018] As stated above, the pipe diameter D1 for the profiles of the Fig. 2, Fig. 3A and Fig. 3B 6 mm and the flow rate is 0.3 l / min. The condensing vapor is water, the carrier gas is air, and the incoming flow is at 22°C and 50% relative humidity (RH). Fig. In the layer shown in Figure 2, the current reaches a maximum saturation ratio of 1.42. The maximum occurs at a distance of approximately one-sixth of a pipe radius from the centerline to the colder wall.

[0019] Fig. Figure 3A shows the axial dependence of the saturation ratio for several radial positions along the axis at y = 0 of Fig. 2 positioned xz-plane. The saturation ratio at the inner walls is always equal to 1, since the boundary conditions for wetted walls apply, and any excess water vapor would simply condense. Saturation ratios in the core of the flow increase rapidly at the inlet 115 of the tube, initially increasing at distant radial positions near the walls, and more slowly near the centerline. Downstream, these saturation ratios reach a plateau of values ​​that depend on the radial position, essentially independent of the axial coordinate. In particular, in this example, the saturation ratio reaches a nearly constant value at each track after a downstream distance of approximately 25-40 mm. Except at the walls, these plateau saturation values ​​are greater than 1.This axial position, at which the saturation ratio plateaus are proportional to the flow rate, and more generally the product of this axial distance and the volumetric flow rate, falls in the range of 0.5 to 0.8 s / cm. 2 As noted above, the highest saturation ratios are reached somewhat away from the centerline. Fig. Figure 3B shows saturation ratios achieved for the same configuration and operating temperatures when the incoming stream is completely dry, at 0% RH. After reaching the maximum supersaturation of 1.42, this does not change significantly from the maximum supersaturation for the case where the incoming stream was at 50% RH.

[0020] Fig. Figure 4 illustrates a second embodiment of the present technology configured as a flat coiled growth tube 400. The growth tube 400 is a single-plane coiled tube, with the top surface being warmer than the bottom. Air enters in the center at the narrower radius and travels along the coil, exiting at the outer edge, as indicated by the arrows. A lighter shade indicates warmer temperatures, according to the scale to the right (values ​​in °C).

[0021] Although not shown in detail in a separate cross-section, the embodiment of Fig. 4 areas 410 and 412 in a similar manner to that of the embodiment of Fig. 1: The wall in region 410 is maintained at 60°C at angular positions from approximately 20° to 160°, and the wall in region 412 is maintained at 20°C at angular positions from 200° to 340° in region 112. The angular positions are referenced to a common origin, and the angular positions (the origin) and thus regions 410 and 412 are constant and thus extend longitudinally over the length of tube 400.

[0022] In Fig. 4, the top surface 410 is warmer than the bottom surface 412. Air enters the center at the narrower radius at inlet 415 and moves along the coil, exiting at the outer edge. A lighter shade indicates warmer temperatures according to the scale to the right (values ​​in °C).

[0023] The spiral geometry leads to the development of a secondary current pattern, as in Fig. 5. In Fig. 5 show velocity fields in the helix secondary flow pattern, with the center of the helix to the left of the cross section of Fig. 5. Dashed lines show the secondary flow pattern, which is the component of the flow perpendicular to the pipe axis, i.e., in the plane of the drawing. The length of each dash is proportional to the magnitude of the velocity. The arrows indicate the direction of the secondary flow. Solid lines are contours of constant velocity for the primary flow moving axially along the pipe. The direction of the flow for cross-section 5-5 in Fig. 4 extends out of the plane of the drawing. As shown, the flow pattern is not turbulent; that is, the flow velocity does not change with time, but only changes spatially. However, instead of the straight flow paths that generally characterize laminar flow, the flow paths in the helix geometry are not straight. Instead, the paths follow a helical pattern that brings flow from the cold and warm walls directly into the center of the flow. The center of the helix is ​​further to the left. The solid lines show the contours of equal longitudinal flow, that is, along the axis of the tube. These longitudinal velocities are slightly greater towards the outside of the helix. The dotted lines show the normal flow components, which exhibit a double vortex pattern. Individual flow paths follow a double helix that becomes streamlined for part of the time following the wall, curves towards the center, and returns to the outside.

[0024] The extent of the displacement of the longitudinal flow maximum from the center of the tube and the size of the vertical vortex pattern with respect to the longitudinal velocities depends on the Dean number defined as follows: De=ReAD where Re=ρVDμ is the Reynolds number, V is the mean flow velocity, D is the tube diameter, A is the helix diameter, ρ is the air density, and µ is the air viscosity. The helix diameter A is twice the distance from the central axis of the helix to the center of the tube. In the helical configuration, A is constant, whereas in the flat spiral configuration, A is smaller near the center of the helix. For small De<17, i.e., when the helix radius is large compared to the tube diameter, a pair of symmetrically placed counter-rotating vortices is formed as a result of the centrifugally induced pressure gradient. The secondary flow pattern can be described analytically as in Dravid, AN, Smith, KA, Merrill, EW, Brian, PLT, “Effect of secondary fluid motion on the laminar flow heat transfer in helically coiled tubes,” American Institute of Chemical Engineering Journal 17: 1114-1122, 1971.For moderate values, De<370, the double vortex inside the pipe becomes asymmetric. At higher velocities in the outer vortex, however, the flow paths are well-defined and time-invariant. At higher De, the flow begins to separate from the inner wall of the pipe. The modeling presented above applies to the case of De=350.

[0025] The resulting geometry is advantageous for generating the vapor supersaturation required for condensation growth, as the secondary flow patterns enhance the transport of vapor from the wetted walls to the center of the flow. An air parcel near the center of the tube will eventually migrate near the wall, improving heat and vapor transfer. This effectively shortens the diffusion distance, and the saturation ratio returns to a steady-state value, which depends primarily on the radial location. After reaching steady-state, the saturation ratio plateaus at a nearly constant value, providing sufficient time for particle activation and growth.

[0026] The Fig. 6, Fig. 7A and Fig. 7B show the saturation conditions that occur in the embodiment of Fig. 5 can be achieved, with the helix radius R = A / 2 (pipe centerline measured to a 180° pipe centerline) varying from 7 to 17 mm. Calculations are based on a 120 mm long pipe with a 6 mm diameter and a flow rate of 0.3 l / min.

[0027] Fig. 6 represents the saturation ratio for a layer of current located between the warm and cold surface of the growth tube of Fig. 4, where a lighter shade indicates higher values ​​of the saturation ratio, as shown in the scale to the right. The pipe diameter D1 is 6 mm, and the flow rate is 0.3 l / min. The condensing vapor is water, the carrier gas is air, and the incoming stream is at 22°C and 0% RH.

[0028] Fig. Figure 7A shows the saturation ratio at several radial positions from the vertical layer of Fig. 4, where the incoming stream is at 22°C and 0% RH. Fig. Figure 7B shows the saturation ratio at several radial positions from the vertical layer of Fig. 4, with the incoming stream at 22°C and 50% RH. Note that this vertical slice extends from the warmer surface through the centerline of the tube to the cooler surface, and further, that it extends along the tube axis from the stream inlet to the stream outlet.

[0029] The flow enters near the center at inlet 415 at the narrower radius of the coil. For comparison, calculations were made at the same operating temperatures, flows, and tube diameters as for the straight configuration of Fig. 1. The result shows the same general properties of the embodiment of Fig. 4 as for the straight tube design of Fig. 1, although the maximum supersaturation achieved is 1.50, which is slightly higher than the 1.42 for the straight tube. Thus, the secondary flow, which brings flow from more distant radial positions to the center, improves the supersaturation. As with the straight growth tube sandwich approach, the maximum saturation is essentially independent of the relative humidity of the incoming flow, with calculations for sampling at either 0% RH or 50% RH, both of which yield a saturation ratio of 1.52.

[0030] One in the Fig. 8A and Fig. The third embodiment shown in Figure 8B is a helical coil 700. In this helical growth tube with a spiral coil, the inner and outer surfaces of the coil are at different temperatures, as indicated by the shading. In this example, the inner surface is at 60°C and the outer surface is at 20°C. Carrier gas enters at inlet 720 and exits at outlet 721. This embodiment can be more compact for cases where it is necessary to handle a larger sample flow rate. The given example has a tube diameter D2 of 10 mm, a coil diameter A2 of 40 mm, and an air flow rate of 7 l / min. The inner surfaces of the coil are maintained at 60°C and the outer surfaces at 20°C. Fig. 8B contains the embodiment of the Fig. 8A and Fig. 8B areas 710 and 712, which correspond to 110 and 112 (rotated by 90°) in a manner similar to that of the embodiment of Fig. 1 are equivalent: the wall in region 710 is held at 60°C for an arc length of 140°, and the wall in region 712 is held at 20°C for angular positions of 140°, although longer or shorter arc lengths may be used. The angular positions are referenced to a common origin, and the angular positions (the origin), and thus regions 710 and 712, occupy the same angular positions relative to the origin at every cross-section of the tube over the length of tube 400.

[0031] Fig. 9 represents the saturation ratio for the layer located between the warm and cold surface of the growth tube of the Fig. 8A-8B and passes through its centerline. A lighter shade indicates a higher saturation ratio value. Note that the saturation ratio quickly reaches a value above 1.2, which is then maintained along the length of the coil. The condensing vapor is water, the carrier gas is air, and the incoming stream is at 20°C and 30% RH.

[0032] The degree of saturation achieved with this configuration is Fig. 10 shown. Fig. Figure 10 shows the saturation ratio as a function of axial position for several radial positions for the helix sandwich configuration of the Fig. 8A-8B. In this example, the maximum saturation ratio is 1.3, which is lower than that achieved with the flat coil at the same operating temperatures. This lower value is likely due to the temperature differential not matching the recirculation flow pattern, as was the case with the flat coil.

[0033] The advantage of the sustained saturation ratio regime is to provide more activation time and produce larger droplets while maintaining the smaller tube diameters required to avoid saturation degradation at high particle concentrations due to condensation heat loss.

[0034] In all of the above examples, the case of water condensing onto particles suspended in air was considered. In this case, the diffusivity of the condensing fluid and the thermal diffusivity of the carrier gas are similar, as is the case, for example, with water condensing onto particles entrained in air. Because water is a small molecule, it diffuses faster than the temperature increases. In particular, the mass diffusivity of water vapor at room temperature is 0.25 cm 2 / s, while the thermal conductivity of air is 0.20 cm 2 / s. When both heat and water diffuse from the walls into the flow, the transport of water vapor overtakes the transport of heat. The result is a water vapor supersaturation region near the centerline.

[0035] The same approach can also be used for cases where the diffusivities are more varied, such as the condensation of isopropyl alcohol on particles in an air stream. In this case, the point of maximum supersaturation is farther from the centerline of the stream than for water condensation. However, as in the examples shown, the degree of supersaturation along each trajectory reaches a nearly constant value, providing sufficient time for particle activation and growth.

[0036] The Fig. 11A-11B illustrate the use of the flat coil growth tube in conjunction with a particle counter 1114b or as a particle collector 1114a. The flat coil or spiral growth tube 1120 is formed by two symmetrical plates 1105, 1107 into which a groove 1120a is formed, as in Fig. 11c and Fig. 11d. (It should be noted that an opposite and opposing groove, not shown, is cut into an upper metal plate 1105 to complete the formation of the tube 1120.) These are then joined together as shown in Fig. 11b. A small heater 1104, such as a cartridge or foil heater, is attached to one side, and a cooler 1106, such as a Peltier or thermoelectric device, is attached to the other. Alternatively, a single thermoelectric element can be mounted between the two plate halves 1105, 1107 to pump heat from one side to the other. Insulation between the two halves reduces heat leakage between the two plates. By using an unfired alumina biscuit or other wettable material for the construction of the two plates 1105, 1107, into which the groove is cut, it is possible to obtain wetted areas over the entire inner surface of the coil. As shown, the flow enters the inlet 1102 in the center of the coil tube 1120 and flows through the coil, where the ultrafine particles grow by condensation.This growth is due to the vapor supersaturation generated by the relative water and vapor transport rates from the wetted, non-isothermal walls, as explained above.

[0037] Depending on the desired application, the current is directed to an optical sensor 1114b or to an impactor collector 1114a, as shown in the Fig. 11C and Fig. 11D. When coupled to the optical sensor 1114d, the device forms a condensation particle counter that detects and measures the concentration of individual ultrafine particles suspended in a stream of air or other gas. When coupled to an impactor collector 1114a, the device becomes an ultrafine particle collector that deposits ultrafine particles as a concentrated spot or set of spots on a solid surface. Particle collectors can also deposit in liquid. In both applications, the detection or capture of the ultrafine particles is enabled by condensation growth. In addition to collecting and counting, the condensation growth method set forth here can be used to enhance electrical charging or to aerodynamically focus the particles. Although the Fig. 11A-D have shown these applications using the flat spiral growth tube, these identical concepts also apply to the Fig. Helix configuration shown in Figure 8.

[0038] In an alternative embodiment, an insulating layer may be provided between plates 1105 and 1107. In such embodiments, the insulating layer may be formed of plastic or foam and may have a groove that aligns with the groove formed in each of the plates. The resulting tube formed by plates 1105 and 1107 with the insulating layer need not be completely circumferential (circular), but may instead have a cross-section resembling an oval shape.

[0039] The coil approach can also be applied to the laminar flow water condensation process of Hering et al. (U.S. Patent 6,712,881 and U.S. Patent 8,801,838), in which a stream flows laminarly through a region where the walls are moist and the temperature is higher than the temperature of the incoming stream. Within this warm, moist-walled section, the water vapor diffuses into the cooler stream faster than it warms up, creating a water vapor supersaturation region with a maximum in the middle part of the stream. This can be preceded by a conditioning stage to control the temperature of the incoming stream, or followed by a moderation stage to remove water vapor from the stream once supersaturation is achieved, or all three stages can operate in concert. Any of these three approaches can be adapted to the coil approach.Due to the secondary flow patterns discussed above, the coil both improves the transport rate from the walls and provides a more compact design.

[0040] Fig. Figure 12 shows the application of the present technology to the process of US Pat. No. 6,712,881, which includes a growth tube coil with a cooled conditioner followed by a warm growth zone. The air is cooled and humidified in the lower 1.5 turns and then encounters a 30°C warmer temperature—the growth zone—over a full turn, during which the saturation ratio reaches 1.4.

[0041] Fig. Figure 13 shows a model comparison between a straight growth tube and a spiral growth tube. To accommodate 7 l / min, the straight version is 2 meters long. The spiral version requires significantly less tube length. Fig. Figure 13 shows the calculated saturation ratio along the centerline for this geometry, determined by numerical modeling. These results apply to a pipe with a diameter of 10 mm carrying a flow of 7 l / min. Furthermore, Fig. 13 shows the coil design with the straight growth tube according to the method of US Patent 6,712,881. Both are designed to carry the same flow rate of 7 l / min. The peak saturation ratio of the coiled tube is slightly compromised, but fulfills its function in less than one-third of the tube length. Fig. Figure 13 shows a comparison of the coiled growth tube and the straight growth tube implementation. In this case, the straight version has been broken into several parallel growth tubes, as would be done to limit the length of an instrument. The coiled version has approximately one-fifth the volume.

[0042] Each of the design approaches described herein utilizes variable flow rates and tube diameter components, providing non-turbulent flow in the various embodiments of the device described herein. For isothermal flow in a tube, this requirement can be met by selecting the tube diameter and flow such that the Reynolds number defined above is below 2000. For the coil geometry, there is an additional requirement that the Dean number be below approximately 500. For temperature differences, it is also necessary to select the tube diameter to ensure that natural convection is low compared to forced convection. Natural convection refers to the flow resulting from a vertical density gradient created by a temperature difference in the system.The relative magnitude of natural to forced convection is described by the dimensionless group denoted by the Froude number, which is defined as follows:. Fr=(ρV2) / (ρV02)=(ρV2) / (Δρ g L), where V is the characteristic velocity for forced convection, V0 is the characteristic velocity for natural (or free) convection, ρ is the air density, Δρ is the change in air density due to a temperature difference, g is the gravitational constant, and L is the characteristic distance, while for small Fr, natural convection dominates. For the above systems, the characteristic distance L is the axial distance over which the temperature jump at the inlet occurs, which in the given examples is the pipe diameter. The systems presented above all use small pipe diameters with respect to the temperature difference, so that Fr>1. This consideration is of less importance when the flow is within a horizontal pipe with the warm surface at the top, as for example in the Fig. 1A-1B and Fig. 4A-4B shown.

[0043] In summary, the advantages of a coil geometry for improving the generation of a vapor supersaturation region and its application to condensation growth for small suspended particles are described herein. In particular, it has been demonstrated that the coil geometry can be used in a "sandwich" configuration, where one side of the tube forming the coil or helix is ​​warmer than the other. The sandwich geometry, whether coiled or not, ensures sustained high supersaturation levels, which can promote droplet growth even when the tube diameter is small. Furthermore, it provides more time for the activation of condensation growth, a feature that can improve the initiation of growth on less wettable particles.

[0044] A successful application of these concepts requires non-turbulent flow. For tubular geometries, these criteria are met under the conditions of Re<2000, Fr>1. In the calculations presented above, the Re ranged from approximately 70 to 1000, and Fr ranged from approximately 4 to 200. However, it should be noted that for the flat tube configuration with the warmer surface at the top, the flow is stable and not disturbed by buoyancy even at small values ​​of Fr. For the helical geometry, the literature cited herein states that the Dean number should be less than 370 to prevent flow separation from the inner wall. The calculations presented above for the “snail” configuration of Fig. 4 meet these criteria with a De in the range of 100-170. In the helix configurations of Fig. 8 and Fig. However, calculations were performed at higher De values ​​in the range of 2000–3000, as our numerical model takes such flow separation into account. Operation at higher De temperatures still ensures an improvement in the supersaturation profile. Thus, configurations with higher De values ​​are acceptable for this application.

[0045] The condensation process of the growth tube coil mentioned above can be described as in the Fig. 14A and Fig.14B. A tube 1400 with a diameter D is arranged in a coil. At any point along the coil, a coil diameter A is defined as twice the distance from the central axis of the coil to the center of the tube. The tube has an inlet and an outlet through which the carrier gas is passed. Most often, this carrier gas is air. The inner walls of the tube are wetted with a condensable fluid, such as water. When viewing a cross-section of the tube, the temperature along a first portion of the circumference 1410 is controlled to a value T h while the temperature along a second part of the circumference 1412 is reduced to a value T c These two circumferential parts extend along a length of the pipe. The temperature T h is higher than the temperature T c, but lower than the boiling point of the condensable fluid at the flow pressure within the tube. The intermediate sections of the circumference 1418 and 1419 have temperatures somewhere between T h and T c The inlet section to this growth tube may be a tubular section 1420 that is thermally insulated from the growth tube. An outlet section 1421 may also be present, which may be thermally insulated from the growth tube. The outlet section may be a straight tube to minimize inertial deposition of droplets formed by condensation growth. It should be noted that the tube cross-section does not need to be completely circumferential, but may include a circular, oval, or any arcuate surface.

[0046] The above description describes these circumferential sections in terms of their angular position relative to the central axis of the tube. Calculations are presented for which the first circumferential section is described by angular coordinates of 20–160° relative to the line in the center of the tube, and the second circumferential section is described by angular positions of approximately 200–340°, with these angular coordinates relative to the central axis of the tube. In the given examples, these angular positions are constant along the length of the tube. However, it is clear that the saturation profiles, and thus the condensation growth of the suspended particles in the stream, will be essentially the same even if these angular positions vary somewhat along the length of the tube or if the tube is not perfectly round. A slightly oval shape will produce a similar result.The method presented here is expected to form vapor supersaturation regions in any configuration in which a flow is maintained between two wetted surfaces at different temperatures and separated along a direction perpendicular to the flow.

[0047] A system using this growth tube coil is coupled at its outlet to a droplet measurement or manipulation device 1430, such as a particle counter or collector, or a particle focuser or loader. A pump, fan, or air mover 1440 may be provided. When a particle-containing stream is introduced into the system, the particles grow by condensation onto the particles of the condensable fluid used to wet the walls. This condensation growth enlarges the particles by a few nanometers to form droplets that have a diameter in the micrometer range or larger. The enlarged particles are much more easily counted by an optical device, collected by an inertial device, aerodynamically focused, or electrically charged.Thus, any number of particle devices can be coupled to the outlet of the growth tube coil to allow the measurement or manipulation of small particles more easily than would be possible without their magnification.

[0048] After enlarging the particles through condensation growth, they can be more easily detected or manipulated than the original ultrafine particle. There are many examples of the application of condensation growth to enable optical detection of particles, such as in condensation nucleus counters or condensation particle counters. There are also many examples of the application of condensation growth to particle collection, particularly to enable chemical or biological analysis. Furthermore, condensation growth is used to aerodynamically focus and concentrate particles or to electrically charge them more efficiently. All of these applications can be used with the sustained condensation growth method presented here.The continued condensation growth even allows the formation of larger droplets, which are even more easily detected optically, collected by inertia, or aerodynamically focused.

[0049] Although the subject matter has been described in terms specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed by way of example for implementing the claims.

Claims

[1] Apparatus designed to produce enlarged particles by condensation growth in a stream, comprising: a tubing coil having an inner surface defining a tubing cross-section, the tubing coil having a coil diameter (A), the tubing (1400) having a current-receiving inlet and an outlet, the tubing (1400) having a length between the inlet and the outlet; a heater (1104) configured to heat the tube (1400) along a first longitudinal portion of the tube cross-section, the first longitudinal portion of the tube cross-section having a first arcuate location relative to a cross-section of the tube (1400) along the length of the tube (1400); and a cooler (1106) configured to cool the tube (1400) along at least a second longitudinal portion of the tube cross-section, wherein the second longitudinal portion of the tube cross-section has a second arcuate location with respect to a cross-section of the tube (1400) along the length of the tube (1400). [2] The device of claim 1, wherein the inner surface is adapted to be wetted with a condensing fluid. [3] The device according to claim 1, wherein the tube (1400) has a circular cross-section and both a first part of the tube (1400) and a second part of the tube (1400) have an arc length in a range of 130 to 170°, wherein the first part of the tube (1400) and the second part of the tube (1400) are separated by transition regions of equal arc length. [4] The device of claim 1, wherein the device is formed by a first and a second planar plate (1105, 1107), each plate (1105, 1107) having a groove formed therein, the groove having a semi-circular cross-section, thereby forming a circular cross-section for the tube when the first and second plates (1105, 1107) are joined together. [5] The device of claim 4, wherein the first and second plates (1105, 1107) are formed of a wettable material. [6] The device of claim 3, wherein the first part and the second part of the tube (1400) are arranged in opposed relationship with respect to the circumference of the tube (1400), the coiled tubing being formed in a plane, the plane defining an origin on one side of the circumference of the tube (1400), the first part having an axial position between 20 and 160° with respect to the origin, the second part having an axial position between 200 and 340° with respect to the origin. [7] The device of claim 3, wherein the first part and the second part are arranged in opposing relationship with respect to the circumference of the tube (1400) and with respect to an origin, the coiled tube being formed in a helix, the origin being aligned in a plane parallel to an axis passing through a center of the helix, the first part having an axial position between 20 and 160° with respect to the origin, the second part having an axial position between 200 and 340° with respect to the origin. [8] A method for enlarging particles, comprising: Providing a tubular coil having a tubular cross-section and a coil diameter, wherein the tube (1400) has an inner surface with an inlet configured to receive a current, and an outlet, the tube (1400) having a length between the inlet and the outlet; Wetting the inner surface with a condensing fluid over the entire tubing coil; Heating the tube (1400) along a first longitudinal portion of the tube cross-section, the first portion of the tube cross-section having a first arcuate cross-sectional location along the length of the tube (1400); simultaneously with the heating, cooling the tube (1400) along at least a second longitudinal portion of the tube cross-section, wherein the second portion of the tube cross-section is located at a second arcuate cross-sectional location along the length of the tube (1400); and Introducing the current into an interior of the tube (1400) at the inlet, wherein the current moves towards the outlet. [9] The method of claim 8, wherein the method comprises wetting the inner surface with water. [10] The method of claim 9, wherein the tube (1400) has a cylindrical cross-section and the method comprises heating both the first part of the tube (1400) and the second part of the tube (1400) by heating opposite sides of the tube (1400) in an arc length in a range of 130-170°. [11] The method of claim 9, wherein heating the first part and cooling the second part of the tube (1400) such that the first part and the second part are in opposing relationship with respect to the circumference of the tube (1400), the coiled tubing being formed in a plane, the plane defining an origin on one side of the circumference of the tube (1400), and heating the first part at an axial position between 20 and 160° with respect to the origin and cooling the second part at an axial position between 200 and 340° with respect to the origin. [12] The method of claim 9, wherein heating the first part and cooling the second part of the tube (1400) such that the first part and the second part are arranged in opposing relationship with respect to the circumference of the tube (1400) with respect to an origin, the coiled tubing being formed in a helix, the origin being aligned in a plane parallel to an axis traversing a center of the helix, comprises heating the first part to form the first part at an axial location between 20 and 160° with respect to the origin, and cooling the second part to form the second part at an axial location between 200 and 340° with respect to the origin. [13] The method of claim 9, wherein the step of introducing comprises providing a particle-containing stream at a temperature of about 20-25°C. [14] The method of claim 8, wherein heating comprises heating the first part to a temperature of about 60°C. [15] The method of claim 8, wherein cooling comprises cooling the second part to a temperature of about 20°C. [16] A method for enlarging particles in a stream, comprising: Introducing the flow into a coiled tubing having a wetted inner surface, the tubing (1400) being configured to conduct the flow in an axial direction along the inner surface of the tubing (1400); and Controlling the inner surface temperatures of the tubing coil at cross-sectional angular positions of the tube (1400), wherein the controlling provides arc wall temperatures in opposite axial regions of the tube (1400) over a majority of the length of the tube (1400), wherein the difference in arc wall temperatures is at least 30°C. [17] The method of claim 16, wherein the step of controlling comprises: Heating a first axial region of the tube (1400) along a first portion of a tube diameter, the first portion of the tube diameter having a first angular position along the length of the tube (1400); and simultaneously cooling a second axial region of the tube (1400) along at least a second portion of the tube diameter, wherein the second portion of the tube diameter is in a second angular position along the length of the tube (1400). [18] The method of claim 17, wherein heating comprises heating the first axial region of the tube (1400) such that the first axial region occupies an axial position between 20 and 160°C with respect to an origin, and cooling comprises cooling the second axial region such that the second axial region occupies an axial position between 200 and 340° with respect to the origin, the origin being aligned in a plane through the center of the plane of the tubing coil. [19] The method of claim 17, wherein heating comprises heating the first axial region of the tube (1400) such that the first axial region occupies an axial position between 20 and 160°C with respect to an origin, and cooling comprises cooling the second axial region such that the second axial region occupies an axial position between 200 and 340° with respect to the origin, wherein the coiled tubing is formed as a helix, the origin being aligned in a plane parallel to an axis passing through a center of the helix. [20] The method of claim 16, wherein the method comprises wetting the inner surface with water.

Images